1,244 research outputs found
Monte Carlo simulation method for Laughlin-like states in a disk geometry
We discuss an alternative accurate Monte Carlo method to calculate the
ground-state energy and related quantities for Laughlin states of the
fractional quantum Hall effect in a disk geometry. This alternative approach
allows us to obtain accurate bulk regime (thermodynamic limit) values for
various quantities from Monte Carlo simulations with a small number of
particles (much smaller than that needed with standard Monte Carlo approaches).Comment: 13 pages, 6 figures, 2 table
Neutral Collective Excitations in Striped Hall States
In the striped Hall state, a magnetic translation in one direction is
spontaneously broken to the discrete translation. The spectrum of the neutral
collective excitation is obtained in the single mode approximation at
half-filled third and fourth Landau levels. The spectrum is anisotropic and has
a multiple line node structure. In one direction, the spectrum resembles the
liquid Helium spectrum with the phonon and roton minimum.Comment: 2 pages, 2 figures, LT23 Hiroshim
Comparison of Grammar in Neurodevelopmental Disorders: The Case of Binding in Williams Syndrome and Autism With and Without Language Impairment
This study investigates whether distinct neurodevelopmental disorders show distinct patterns of impairments in particular grammatical abilities and the relation of those grammatical patterns to general language delays and intellectual disabilities. We studied two disorders (autism and Williams syndrome [WS]) and two distinct properties (Principle A that governs reflexives and Principle B that, together with its associated pragmatic rule, governs pronouns) of the binding module of grammar. These properties are known to have markedly different courses of acquisition in typical development. We compare the knowledge of binding in children with autism with language impairment (ALI) and those with normal language (ALN) to that of children with WS, matched on age to the ALN group, and on age and nonverbal mental age (MA) to the ALI group, as well as to two groups of typically developing (TD) controls, matched on nonverbal MA to ALI and ALN groups. Our results reveal a remarkably different pattern of comprehension of personal pronouns and reflexives in ALI as opposed to ALN, WS, and two groups of TD controls. All five groups demonstrated an equal delay in their comprehension of personal pronouns, in line with widely reported delays in TD literature, argued to be due to delayed pragmatic abilities. However, and most strikingly, the ALI group also showed a pronounced difficulty in comprehension of reflexive pronouns, and particularly of the knowledge that the antecedent of a reflexive must c-command it. The revealed pattern confirms the existence of a particular impairment concerning Principle A in this module of grammar, unrelated to general language delays or cognitive deficits generally present in a large portion of individuals with autism as well as WS, or to general pragmatic deficits, known to be particularly prevalent in the population with autism
The Onset of Anisotropic Transport of Two-Dimensional Electrons in High Landau Levels: An Isotropic-to-Nematic Liquid Crystal Phase Transition?
The recently discovered anisotropy of the longitudinal resistance of
two-dimensional electrons near half filling of high Landau levels is found to
persist to much higher temperatures T when a large in-plane magnetic field B||
is applied. Under these conditions we find that the longitudinal resistivity
scales quasi-linearly with B||/T. These observations support the notion that
the onset of anisotropy at B||=0 does not reflect the spontaneous development
of charge density modulations but may instead signal an isotropic-to-nematic
liquid crystal phase transition.Comment: 5 pages, 4 figure
Weak charge form factor and radius of 208Pb through parity violation in electron scattering
We use distorted wave electron scattering calculations to extract the weak
charge form factor F_W(q), the weak charge radius R_W, and the point neutron
radius R_n, of 208Pb from the PREX parity violating asymmetry measurement. The
form factor is the Fourier transform of the weak charge density at the average
momentum transfer q=0.475 fm. We find F_W(q) =0.204 \pm 0.028 (exp) \pm
0.001 (model). We use the Helm model to infer the weak radius from F_W(q). We
find R_W= 5.826 \pm 0.181 (exp) \pm 0.027 (model) fm. Here the exp error
includes PREX statistical and systematic errors, while the model error
describes the uncertainty in R_W from uncertainties in the surface thickness
\sigma of the weak charge density. The weak radius is larger than the charge
radius, implying a "weak charge skin" where the surface region is relatively
enriched in weak charges compared to (electromagnetic) charges. We extract the
point neutron radius R_n=5.751 \pm 0.175 (exp) \pm 0.026 (model) \pm 0.005
(strange) fm$, from R_W. Here there is only a very small error (strange) from
possible strange quark contributions. We find R_n to be slightly smaller than
R_W because of the nucleon's size. Finally, we find a neutron skin thickness of
R_n-R_p=0.302\pm 0.175 (exp) \pm 0.026 (model) \pm 0.005 (strange) fm, where
R_p is the point proton radius.Comment: 5 pages, 1 figure, published in Phys Rev. C. Only one change in this
version: we have added one author, also to metadat
Dominant aerosol processes during high-pollution episodes over Greater Tokyo
This paper studies two high-pollution episodes over Greater Tokyo: 9 and 10
December 1999, and 31 July and 1 August 2001. Results obtained with the
chemistry-transport model (CTM) Polair3D are compared to measurements of
inorganic PM2.5. To understand to which extent the aerosol processes modeled in
Polair3D impact simulated inorganic PM2.5, Polair3D is run with different
options in the aerosol module, e.g. with/without heterogeneous reactions. To
quantify the impact of processes outside the aerosol module, simulations are
also done with another CTM (CMAQ). In the winter episode, sulfate is mostly
impacted by condensation, coagulation, long-range transport, and deposition to
a lesser extent. In the summer episode, the effect of long-range transport
largely dominates. The impact of condensation/evaporation is dominant for
ammonium, nitrate and chloride in both episodes. However, the impact of the
thermodynamic equilibrium assumption is limited. The impact of heterogeneous
reactions is large for nitrate and ammonium, and taking heterogeneous reactions
into account appears to be crucial in predicting the peaks of nitrate and
ammonium. The impact of deposition is the same for all inorganic PM2.5. It is
small compared to the impact of other processes although it is not negligible.
The impact of nucleation is negligible in the summer episode, and small in the
winter episode. The impact of coagulation is larger in the winter episode than
in the summer episode, because the number of small particles is higher in the
winter episode as a consequence of nucleation.Comment: Journal of Geophysical Research D: Atmospheres (15/05/2007) in pres
Physics on the edge: contour dynamics, waves and solitons in the quantum Hall effect
We present a theoretical study of the excitations on the edge of a
two-dimensional electron system in a perpendicular magnetic field in terms of a
contour dynamics formalism. In particular, we focus on edge excitations in the
quantum Hall effect. Beyond the usual linear approximation, a non-linear
analysis of the shape deformations of an incompressible droplet yields soliton
solutions which correspond to shapes that propagate without distortion. A
perturbative analysis is used and the results are compared to analogous
systems, like vortex patches in ideal hydrodynamics. Under a local induction
approximation we find that the contour dynamics is described by a non-linear
partial differential equation for the curvature: the modified Korteweg-de Vries
equation.
PACS number(s): 73.40.Hm, 02.40.Ma, 03.40.Gc, 11.10.LmComment: 15 pages, 12 embedded figures, submitted to Phys. Rev.
Negative Electron-electron Drag Between Narrow Quantum Hall Channels
Momentum transfer due to Coulomb interaction between two parallel,
two-dimensional, narrow, and spatially separated layers, when a current
I_{drive} is driven through one layer, is studied in the presence of a
perpendicular magnetic field B. The current induced in the drag layer,
I_{drag}, is evaluated self-consistently with I_{drive} as a parameter.
I_{drag} can be positive or negative depending on the value of the filling
factor \nu of the highest occupied bulk Landau level (LL). For a fully occupied
LL, I_{drag} is negative, i.e., it flows opposite to I_{drive}, whereas it is
positive for a half-filled LL. When the circuit is opened in the drag layer, a
voltage \Delta V_{drag} develops in it; it is negative for a half-filled LL and
positive for a fully occupied LL. This positive \Delta V_{drag}, expressing a
negative Coulomb drag, results from energetically favored near-edge inter-LL
transitions that occur when the highest occupied bulk LL and the LL just above
it become degenerate.Comment: Text file in Latex/Revtex/preprint format, 7 separate PS figures,
Physical Review B, in pres
"Beat" patterns for the odd-even staggering in octupole bands from a quadrupole-octupole Hamiltonian
We propose a collective Hamiltonian which incorporates the standard
quadrupole terms, octupole terms classified according to the irreducible
representations of the octahedron group, a quadrupole-octupole interaction, as
well as a term for the bandhead energy linear in K (the projection of angular
momentum on the body-fixed z-axis). The energy is subsequently minimized with
respect to K for each given value of the angular momentum I, resulting in K
values increasing with I within each band, even in the case in which K is
restricted to a set of microscopically plausible values. We demonstrate that
this Hamiltonian is able to reproduce a variety of ``beat'' patterns observed
recently for the odd-even staggering in octupole bands of light actinides.Comment: LaTeX, 20 pages plus 12 figures given in separate .ps file
Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy
Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated
using an imaging charge-coupled device (CCD) camera. A spatial resolution less
than 15 m has been achieved, which is equivalent to an UCN energy
resolution below 2 pico-electron-volts through the relation . Here, the symbols , , and are the
energy resolution, the spatial resolution, the neutron rest mass and the
gravitational acceleration, respectively. A multilayer surface convertor
described previously is used to capture UCNs and then emits visible light for
CCD imaging. Particle identification and noise rejection are discussed through
the use of light intensity profile analysis. This method allows different types
of UCN spectroscopy and other applications.Comment: 12 figures, 28 pages, accepted for publication in NIM
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